This invention relates to the thermochemical removal of metal from those specific areas of a workpiece surface which contain defects, a process commonly referred to as "spot" scarfing; and, more specifically, to a scarfing nozzle particularly suited for selective, single pass, fin-free spot scarfing wherein a plurality of adjacent nozzles are used corresponding to the width of the desired cut.
In selective spot scarfing, a plurality of abutting individual scarfing nozzles are spaced transversely across the path of movement of the metal workpiece and are selectively operated so as to scarf only those areas containing surface defects, rather than the entire work surface. A necessary requirement in selective spot scarfing is not only that all scarfing cuts must be made fin-free, but also that they neither overlap adjacent cuts nor cause excessively high ridges therebetween. A spot scarfing nozzle capable of individually scarfing randomly located defects in a metal body without forming fins or ridges of unoxidized metal deposits along the boundaries of the scarfing cut is disclosed in my copending application Ser. No. 607,888, filed of even date herewith, the disclosure of which is incorporated herein by reference.
In a preferred embodiment of a spot scarfing machine, a plurality or bank of adjacent scarfing nozzles, each of which is butted, side-by-side, with other like units, is employed in order to increase the width of metal surface which may be scarfed in a single pass. Thus, such machine may optionally be used to desurface the entire workpiece or, alternatively, selectively scarf randomly located defects. Such a machine is particularly useful in combination with an automatic control system which signals the appropriate scarfing unit to be turned on and off.
Scarfing with a plurality of individual spot scarfing nozzles, of the type described in my above-mentioned copending application, results in an unscarfed portion of the workpiece remaining in the area where the nozzles butt up against each other. This is due to the fact that the aforesaid individual, fin-free scarfing nozzles produce cuts which are narrower than the width of the nozzle discharge orifice. Thus, if two of these nozzles are aligned side-by-side to make two adjacent cuts in a single pass, an unscarfed area will remain between the cuts. Consequently, if a defect as wide as or wider than the width of the nozzle is to be scarfed, it must be done by making at least two consecutive, partially overlapping cuts. This is uneconomical in terms of time, cost of operation and yield loss.